1. Field of the Invention
The present invention relates to an image forming apparatus, more particularly to image forming apparatuses, such as a copying machine, a facsimile machine, and a printer.
2. Description of the Related Art
Examples of an electrophotographic image forming apparatus include an MFP (Multi Function Peripheral) having a scanner function, a facsimile function, a copying function, a function as a printer, a data communication function, and a server function, a facsimile machine, a copying machine, and the printer.
A demand for reduction of power consumption amount of the image forming apparatus including the MFP is increasing with an increasing worldwide interest in an environment, an increasing energy saving consciousness, and an increasing emission reduction consciousness of carbon dioxide. In order that a user checks whether the image forming apparatus is used by a method contributing power saving (a method that is not contrary to the power saving) or whether power is surely reduced, there is proposed a function of displaying the power consumption amount of the image forming apparatus or a function of providing the power consumption amount of the image forming apparatus to a computer out of the image forming apparatus through a network. However, there has not yet been a technology of accurately measuring or calculating the power consumption amount of the image forming apparatus.
Originally the power consumption amount of the image forming apparatus varies according to an operating state of the image forming apparatus. For example, in a standby state that is a state in which printing can be performed without waiting time, power consumption is greater than that of a power saving state that is a state in which some functions are stopped. A state in which the image forming apparatus performs color printing is greater than a state in which the image forming apparatus performs monochrome printing in the power consumption. The conventional function of displaying the power consumption amount places a high value on user's feeling that the power consumption amount decreases after a predetermined period compared with the previous power consumption amount in the case that the user changes settings related to an energy saving function, such as a setting related to a time necessary to transition to the power saving state or in the case that the image forming apparatus starts a mode in which the monochrome printing is recommended. Accordingly, a little value is placed on accuracy of the displayed power consumption amount, and there are few efforts for improving the accuracy of the power consumption amount.
However, with an increasing sense of crisis over global warming, the situation is changed by a worldwide movement in which the emission reduction of carbon dioxide is promoted with a specific numerical target. For example, generally a reduction amount of the whole management target range is calculated by obtaining “a reduction amount of power consumption” or “an emission reduction amount of carbon dioxide calculated from the reduction amount of power consumption” with respect to each of various facilities, such as an air conditioner and the image forming apparatus, in a management target range of a firm or a office. Additionally, the further improvement is performed to the facility in which the target emission reduction amount is not achieved. As a result, there is a need for the accuracy of the power consumption information provided by the image forming apparatus.
The power consumption amount of each facility or a ratio of the power consumption amount of each facility to the whole power consumption amount depends on a season. For example, the power consumption of the air conditioner depends on the season, while the power consumption of an elevator is substantially kept constant throughout the year. Accordingly, the power consumption reduction amount or the target power consumption amount, which is allocated to each of devices, such as the image forming apparatus, varies in each month, and it is necessary to compare the power consumption reduction amount or the target power consumption amount to that of the same month a year ago. That is, the time in which it is required that the qualitative change in power consumption amount of the image forming apparatus is understandable is changed to the time in which it is required that the quantitative change in power consumption amount of the image forming apparatus is understandable.
For example, Documents 1 and 2 described below disclose a method for obtaining the power consumption amount of the image forming apparatus.
Document 1 discloses a technology of calculating a degree of energy saving based on a printing setting and counting results of the numbers of printed sheets and printed copies. In the technology disclosed in Document 1, the power consumption amount is calculated by an equation of “power consumption=(power consumption A during copy)×(printing operating time X)+(power consumption B during sleep×(sleep time Y)+(power consumption C during facsimile)×(facsimile operating time Z)”. The fixed values A, B, and C may be decided in any way.
In a technology disclosed in Document 2, an AC power from an external power source is converted into a DC power of 24 V by an AC/DC converter, and the power consumption amount of the multi function peripheral is measured by a watt-hour meter directly connected to the AC/DC converter.
There is proposed an image forming apparatus having a function of obtaining the power consumption amount of the image forming apparatus to display or sum up a power usage status in order to assist the power saving effort of the user or the manager.
Conventionally, the power consumption amount of the image forming apparatus is measured by measuring a primary-side (a commercial power source of a transformer of the image forming apparatus) power supply voltage and a load current. For example, in a technology disclosed in Document 3 described below, a time in a power saving mode is measured, virtual power consumption is calculated from the measured time and unit power consumption in a previously-measured normal power mode, and a difference between a virtual power consumption amount in the normal power mode and the power consumption amount in the power saving mode is calculated as a power reduction value of the power saving mode.
Document 4 described below discloses a technology of calculating the power consumption amount by measuring a current and a voltage, which are supplied from the commercial power source to the image forming apparatus body. In the technology disclosed in Document 4, in the case that the user issues a printing instruction, image data in which image data of power information notification is added to image data of the printing instruction of the user is generated and printed on a predetermined sheet.    Document 1: Japanese Patent Publication Laying-Open No. 2002-304092    Document 2: Japanese Patent Publication Laying-Open No. 2006-39443    Document 3: Japanese Patent Publication Laying-Open No. 2005-132405    Document 4: Japanese Patent Publication Laying-Open No. 2010-5809
However, in the technologies disclosed in Document 1, unfortunately the power consumption amount obtained by the calculation has the low accuracy.
For example, during the copy, the power consumption depends heavily on a copy mode. This is because there are many copy modes. For example, the number of motors used and a kind of the motor vary according to a sheet feeding port through which the sheet used in the copy is fed. Because each of photosensitive bodies of four colors rotates in a color mode while only one-color photosensitive body rotates in a monochrome mode, the power consumption of the motor that rotates the photosensitive body varies largely between the color mode and the copy mode. An operating time of each member depends on a sheet size. The power consumption depends heavily on the voltage or the current from a high-voltage power supply that is one of main constituents of an electrophotographic process. The voltage or the current is decided to a proper value according to a usage environment by what is called image stabilizing control. The power consumption changes by environmental variations, such as a temperature and humidity. In a low-temperature environment, load torques of components, such as a gear and a bearing, increases by hardening of a grease. Accordingly, according to the environment, sometimes it is necessary to prepare different values as a parameter used to obtain the power consumption amount.
Accordingly, the number of parameters, such as the fixed values A, B, and C, which are necessary to calculate the power consumption amount, increase, and impractically a large amount of work and design man-hour are required to fix the many parameters in order to enhance the accuracy of the power consumption amount.
Additionally, the variation in power consumption associated with aging of the image forming apparatus is serious. In the bearing, the photosensitive body, and cleaning members, such as a transfer belt, the load torque is generated by friction and varies by the aging or a durability change. Accordingly, even if the printing is performed in the same operating mode, the current state of the load changes from the state of the load half a year ago or a year ago, and the power consumption also changes.
Therefore, the variation in power consumption associated with the aging of the image forming apparatus cannot be evaluated, even if the fixed value is set according to the usage method (the printing setting) of the image forming apparatus like Document 1. Even if a manufacturer of the image forming apparatus designs the fixed value over time using a trial model of the image forming apparatus, it is necessary to finely adjust the fixed value in the actual image forming apparatus that is mass-produced using a die. Therefore, depending on a correction scale, work to correct the parameter is required after start of the mass production of the image forming apparatus. Sometimes launching of the image forming apparatus is delayed as it takes to much time for the correction work.
In the technology disclosed in Document 2, when the power consumption of each load of the image forming apparatus is measured, it is necessary to provide the watt-hour meter in each load according to magnitude of the power consumption of each load, which results in a problem in that complication of the apparatus is caused.
The power consumption of the image forming apparatus including the MFP has the following characteristics. In the case that the operating state of the image forming apparatus is warm-up, the image forming apparatus continuously consumes the power ranging from hundreds of watts to one thousand and hundreds of watts in order to perform an operation to heat a fixing device to a predetermined temperature. In the case that the operating state of the image forming apparatus is printing, the image forming apparatus continuously consumes the power of hundreds of watts in order to drive the motor used in the printing. At the same time, the image forming apparatus intermittently consumes the power of hundreds of watts in order to perform a temperature control operation of the fixing device. In the case that the operating state of the image forming apparatus is standby, the image forming apparatus continuously consumes the power of tens of watts in a control circuit and the like. At the same time, the image forming apparatus intermittently consumes the power of one thousand and hundreds of watts in order to control the temperature of the fixing device. In the case that the operating state of the image forming apparatus is in power saving modes, such as the sleep mode, the image forming apparatus continuously consumes the small power of several watts for a long time in the control circuit and the like.
When the power consumption in each operating state is viewed from a time axis, the time in the maximum power consumption state has a small ratio, and the time in the minimum power consumption state (the power saving mode) has the largest ratio.
Accordingly, for example, in the case that the power consumption amount is measured in long periods, such as one week and one month, the variation in power consumption increases, and it is necessary for a power consumption measuring device to accurately measure the wide range of power consumption from low power consumption to high power consumption.
For example, when the wide range of power consumption is accurately measured by a power consumption measuring circuit inserted on the primary side, it is necessary that the power consumption measuring circuit have performance equivalent to a general-purpose measuring instrument, which results in a problem in that the configuration of the image forming apparatus becomes complicated and expensive. In the case that the power consumption measuring circuit is inserted on the primary side, it is necessary that a detection circuit in the power consumption measuring circuit and a portion in which a detection result is displayed be electrically insulated, which results in the problem in that the configuration of the image forming apparatus becomes complicated and expensive. Specifically, in the case that the power consumption amount is calculated based on a value, which is obtained by performing the AD (analog-digital) conversion of the primary-side current, because of the large variation in measured current, the high measurement accuracy of the current is hardly obtained in the inexpensive 10-bit AD converter.
Recently, the specific reduction target of the emitted carbon dioxide or the power consumption amount is indicated by the numerical value, the need for the measurement accuracy of the power consumption amount becomes severer. However, the degradation of the measurement accuracy of the power consumption amount due to the wide of measured power range is not considered in the technologies disclosed in Documents 3 and 4.
In the case that the power consumption of the image forming apparatus from the viewpoint of load variation, there are load variations of the kind of the sheet, an installation environment, and the aging in addition to the variation due to the operating state of the image forming apparatus. For example, in the case that attention is paid to the fixing device, the fixing device is deprived of a heat quantity by the sheet in addition to energy necessary to melt and fix toner. Because the heat quantity depends largely on a thickness or a water amount of the sheet, the heat quantity necessary for the fixing device varies according to the kind of the sheet. The load torque of the motor that drives the image forming apparatus depends on the environment. For example, in the low-temperature environment, the power consumption increases due to the hardening of the grease in the motor. Because of the aging of each component of the image forming apparatus, the image forming apparatus in the new state differs from the image forming apparatus after a long period of use in the toad torque, and the power consumption varies.
In the high-voltage power supply necessary for the electrophotographic process, an output voltage or an output current is adjusted by an image stabilizing operation. Therefore, the power consumption of the high-voltage power supply is not kept constant. In order to implement a quiet rotation, a cooling fan does not always rotate, but the rotation of the cooling fan is controlled by monitoring the temperature.
There is a conventional power consumption calculating method, in which an operating mode and a parameter of the power consumption are previously prepared according to the number of documents to be copied or the number of copies to be printed and the power consumption is calculated using the parameter. In the power consumption calculating method, the difference in power consumption due to the difference of the operating mode can be calculated with a certain level of accuracy. However, a large amount of parameters (pieces of information), such as an environmental condition, a durability condition, an image forming condition, the kind of the sheet, and the thickness of the sheet, are required in the case that an absolute value of the power consumption is calculated by the power consumption calculating method, and a large amount of programs are required in order to enhance detection accuracy of the power consumption amount. As a result, development of a large amount of programs and verification work to fix the parameter are generated.
That is, conventionally a proper power measuring method in which a balance between a product cost and a development cost is established is not proposed in order to enhance the detection accuracy of the power consumption of the image forming apparatus.